Use of Fireflow Tests in the Calibration of a Water Distribution System Model

Fireflow (or hydrant flow) tests are frequently used in the calibration process for water distribution system hydraulic models. In such a test, hydrants are opened and flowed at a high flow rate in order to cause high flows and large head losses in the pipes leading to the hydrant. When a system is stressed in this manner, the behavior of the distribution system is more sensitive to factors such as pipe roughness, closed valves, demands, and PRV settings. By comparing field measurements of flow and pressure to model results for the same situation, model parameters can be adjusted (calibrated) to better represent the system behavior. As part of a master plan and hydraulic model development for The Joint Powers Water Board (JPWB) covering the Green River/Rock Springs/Sweetwater County area in southwestern Wyoming, fireflow tests and other field techniques were used to calibrate the detailed model. Approximately 30 fireflow tests were conducted as part of the calibration process. Additional operational information on the water system (water usage, tank levels, pump operation) was collected from the SCADA system. Subsequently, the hydraulic model was applied under the test conditions and parameter adjustments made to bring the model into better agreement with the field results. The method was found to be most effective in identifying unexpected closed valves, adjusting PRV settings and behavior, and to a lesser degree in adjusting roughness coefficients. The logistics, costs, practical experience and the calibration results are discussed herein.